Academic Dissertation to be presented with the assent of the Faculty of Humanities, University of Oulu, for public discussion in Raahensali (Auditorium L 10), Linnanmaa, on September 27th, 2002, at 12 noon.

Abstract

This work was aimed at studying speech perception and auditory
performance in the everyday lives of Finnish-speaking postlingually
severely or profoundly hearing-impaired adults before and after receiving
a multichannel cochlear implant. The association between the formal speech
perception results and auditory performance in everyday life was also
determined, and an effort was made to define how well a smaller sample
represents the nationwide results.

The patient series comprised a nationwide retrospective survey
(N = 67), in which data on hearing level and word recognition were requested
from the hospitals, and a prospective sample from the city of Oulu (N = 20),
in whom hearing level, sentence, word and phoneme recognition and phoneme
confusions were examined using standardised audiometric measures and
formal speech perception tests in a study with a prospective repeated
measure design. Categories of auditory performance in everyday life were
assessed in both samples.

The median sound field hearing level at frequencies of 0.5, 1, 2 and
4 kHz for the subjects in the nationwide survey one year after
the switch-on of the implant was comparable to the level of mild hearing
impairment. All the subjects achieved at least some open-set word recognition auditorily
only (mean 71%, 95% CI 61-81%). The results in the Oulu sample were in
line with the nationwide survey. A majority of the subjects (31/40) was
able to understand conversation without speechreading one year after
switch-on.

Sentence recognition by the subjects in the Oulu sample improved
most during the initial six months after the switch-on of the implant,
whereas word and phoneme recognition improved steadily during the two-year
follow-up period. Estimated average sentence recognition after two years
was 89% (95% CI 71 to 106%), word recognition 73% (95% CI 58 to 87%),
syllable recognition 53% (95% CI 42 to 63%), vowel recognition 80% (95% CI
68 to 92%) and consonant recognition 67% (95% CI 57 to 76%). Confusion of
phonemes took place more in the direction a spectral energy distribution
at higher frequencies. The association between auditory performance in
everyday life and the formal speech perception tests was high
(rs > 0.81, p < 0.0001).

Systematic prospective assessment of speech perception with tests of
differing difficulty is recommended for the follow-up of adult cochlear
implant users.